The OIDC provider is already tracked in iam_oidc_states.provider, so
there is no need for provider-specific session auth methods (GOOGLE,
MICROSOFT). Replace them with a single OIDC auth method.
Signed-off-by: Bryan Frimin <bryan@getprobo.com>
Implements OpenID Connect authentication flow with PKCE, JWT verification, and enterprise-only account restrictions. Adds OIDC service with JWKS caching and state management, HTTP handlers for login/callback flows, GraphQL query for available providers, and sign-in UI integration.
Signed-off-by: Bryan Frimin <bryan@getprobo.com>